Process and apparatus for froth flotation

ABSTRACT

1,058,914. Froth flotation. OUTOKUMPU OY. June 14, 1965, No. 25097/65. Heading B2H. Froth flotation apparatus operating under a common head of vacuum comprises a pre-conditioning and aerating unit 1, into which pulp and gas are introduced via pipes 3, 4, the pulp being fed via a pipe 6 into a flotation chamber 8. Additional gas is introduced via a pipe 13. Froth is collected by a section 10 and directed into a bubble column 19. Preconditioned particles, treated with reagents to be floatable proceed upwards, and unwanted particles downwards, the downward movement being assisted by wash solutions introduced at 21. Final concentrate is drawn into a cyclone 23 for separation of solids and liquids, and concentrate pulp is discharged into a vessel 25 and over a weir 16, vessel 17 and weir 18. Gas separated in the cyclone is directed via a conduit 27 to a vacuum pump. In a further embodiment, five flotation chambers are employed operating under a common head of vacuum. Pulp material is drawn into rough flotation units (28, 29 Fig. 2) and the rough concentrates rise in columns (37, 38) and are combined in a chamber (30), separation of gas being effected in cyclones (41, 42.) Tailing pulp from the chamber (30) is returned to the chamber (28). Further flotation scavenger chambers (31, 32) receive the rougher tailings for further separation and the coarsest tailings are discharged at (53, 54).

R. T. HUKKI PROCESS AND APPARATUS FOR FROIH FLOTATION Feb. 18, 1969 Sheet lFiled May 27, 1966 /A/VE/v me @/5 To 724m: /v/ HUK/w A TTG/(UVEK R. T. HUKKI PROCESS AND APPARATUS FOR FROTH FLOTATION Feb. 18, 1969 Sheet of 5 Filed May 27, 1966 R. m N m W @/5 To 7'4PA /v/ Huff/n @Y QM 71% Feb. 18, 1969 R. T. HUKKI 3,423,175

PROCESS AND APPARATUS FOR FROTH FLOTTION Filed may 27, 196e sheet 5 of s /N VEN 70@ 8f JMW@ A T ToR/VEX United States Patent O 25,097 65 U.S. Cl. 209-164 4 Claims Int. Cl. B03d 1 06 ABSTRACT F THE DISCLOSURE A froth flotation method and apparatus having unit froth llotation elements with closed flotation chambers operating under sub-atmospheric pressure into which feed slurry is introduced to create and maintain a pulp pool hafving a substantially constant top level within the chamber. Gas medium from an outside source under pressure higher than the sub-atmospheric pressure is introduced into the lower part of the pulp pool and dispersed into fine bubbles. In each unit the pulp ilow is directed downward substantially centrally with respect to the rising stream of bubbles. The floating component is collected above the level of the feed inlet and is discharged therefrom while the non-floating component with liquid medium is discharged at a level below that of the -gas introduction. A plurality of such units formed into a closed circuit grouping under common sub-atmospheric pressure is arranged in such a way that the froth produced in a given step is transferred with evacuated gas medium to a separate flotation step performed in a similar unit on a higher elevation to upgrade the concentrate. The tailing product from such re-treatment step is returned by gravity to the former flotation step performed in a unit on a lower elevation.

In the field of so-called vacuum flotation, the Elmore vacuum process and the respective apparatus described in British Patent 17816 (1904) are basic. With this early apparatus, rather astonishing results were obtained over half a century ago.

It Iis well known that liquids such as water can dissolve substantial quantities of gas such as air. In general the quantity of dissolved gas increases roughly linearly with increasing pressure, but decreases normally with an increase in temperature. At the pressure of 760 mm. Hg, one liter of water will dissolve 29.2 cm.3 of air at 0C., and 17.1 cm.3 at 25 C. By doubling the pressure, the indicated gas quantities are doulbled.

It is also well known that after the release of pressure, or by applying vacuum, gas precipitates from a solution selectively on air avid surfaces such as the mineral surfaces `at least partly covered by organic collector reagents. This well known phenomenon is the key for selective separation by flotation carried out under vacuum or partial vacuum.

It has now been found out that in practical flotation operations the quantity of gas so released from the liquid medium under sub-atmospheric pressure conditions is insufllcient for optimum separation of the iloatable component. In order to provide flexibility and simple means to control the llotation process performed under sub-atmospheric pressure conditions, additional gas medium must be introduced into the pulp processed. As soon as this is done, the flotation process is well under control to any desired degree.

The main basic steps of the froth flotation process described in this specilication are:

3,428,175 Patented Feb. 18, 1969 Establishing and maintaining sub-atmospheric pressure within a closed llotation chamber,

Introduction of feed slurry into the said flotation chamber,

Creation of a pulp pool having substantially constant top level within the said chamber,

Introduction into the lower part of the said pulp pool of additional gas medium originating from an outside source under pressure higher than the said sub-atmospheric pressure acting within the said flotation chamber,

Dispersion of the additional gas medium into line bubbles,

Directing the pulp llow downward in a substantially counterc'urrent fashion against the rising stream of bubbles,

Collecting the iloating component above the level of feed inlet in an upward rising -bulblble column,

Discharging the said froth product, and

Discharging the non-floating component with the balance of the liquid medium via a level below the level of introduction of the additional gas medium. Preconditioning of the suspension to be processed serves a double purpose, i.e. changing the surfaces of the mineral or minerals to be lloated air avid with proper reagents -While the other minerals remain water avid, and dissolving gas, normally air, into the liquid forming the suspension with the solids processed. The roles played, methods applied and quantities used lwhen dealing with flotation reagents such as collectors, frothers and modifying agents are well known to a specialist in the art. They are not discussed in this specification.

The apparatus for the froth flotation process outlined above comprises essentially:

A non-mechanical flotation chamber,

Means to establish and to maintain sub-atmospheric pressure within the said flotation chamber,

Means to introduce feed slurry at a desired rate into thel said llotation chamber,

Means to create a pulp pool haiving substantially constant top level within the said chamber,

Means to introduce at a desired rate additional gas medium into the lower part of the said pulp pool,

Means to disperse the said additional gas medium into line bubbles,

Means to direct the pulp llow downward in a substantially countercurrent fashion against the rising stream of bubbles,

Within the said flotation chamber a columnar upward directed extension above the level of feed inlet,

Means to collect and discharge the concentrate product,

Below the level of feed inlet a downward directed extension to collect the non-floating component with the balance of liquid medium, and

Means to discharge it as a tailing product.

For the creation and maintenance of desired vacuum within the separation chamber, a variety of suitable vacuum pumps are available.

Introduction of the aerated pulp into the separation chamber is performed by controlled injection in a substantially horizontal manner, or by suction from a level below the feed inlet level.

Additional gas medium is introduced into the lower part of the pulp pool at a desired rate from atmospheric air or from any outside source of gas under pressure via any suitable nozzle, bubbler, porous or perforated diffuser made of any suitable material. Injection of air-water mixture under pressure via a suitable injector has been -found to provide extremely simple means to produce linely divided air-in-water dispersion. Injection of air-pulp mixture under pressure is also possible.

The flotation process according to the present invention comprises closed circuit grouping of unit flotation processes to separate the lloatable component from the nonfloatable component in a liquid medium under common sub-atmospheric pressure by means of gas bubbles originating partly -by precipitation of gas dissolved in the liquid medium, and partly by simultaneous dispersion of additional gas introduced from an outside source, the said grouping being arranged in such a way that the froth product produced in a given step is transferred with the evacuated gas medium to a separate retreatment otation step performed on a higher elevation and producing a higher grade concentrate, while the tailing produce produced in the latter retreatment step is returned by gravity to the former floation step performed on a lower elevation.

Other objects, features and advantages of the present invention will be indicated with a reference to the accompanying drawings illustrating the preferred embodiments ol this invention.

In the drawings:

FIGURE 1 is a diagrammatic vertical cross-sectional View showing the details of the unit apparatus constructed in accordance with the principles of this invention.

FIGURE 2 is a similar view showing another possible arrangement of the apparatus.

FIGURE 3 is a similar view showing still another possible arrangement of the apparatus.

FIGURE 4 is a diagrammatic vertical side view showing grouping of the components for a multiple-step closed circuit flotation apparatus.

Referring to FIGURE l the unit apparatus includes the following:

The flotation apparatus proper is preceded by closed preconditioning and aeration unit 1 provided with -mechanically impeller 2. For introduction of pulp under pressure conditioner 1 is equipped with inlet pipe 3 and for introduction of gas similarly under pressure with pipe 4. The rate of gas flow is controlled by valve 5. Discharge of pulp from conditioner 1 takes place by pressure difference via conduit 6 controlled by valve 7.

The main body of flotation chamber 8 consists of cylindrical feed section 9, cylindrical bubble column section 10 and conical bottom section 11. To section 11 is attached section 12 provided with one or more injectors 13 for the introduction of additional gas medium, emergency drainage pipe 14 with valve 15, and wash water inlet pipe 16 with valve 17. Section 11 is further provided with open tailing discharge pipe 18 surrounded -by open pipe 19 of larger diameter. Pipes 18 and 19 form a very simple tailing discharge and overflow system controlling pulp level within otation chamber `8. If desired, the top of pipe 18 can be made adjustable in height. For bleeding of the coarsest sand fraction pipe 18 has been provided with opening 20 controlled by plug 21.

In the case shown, additional gas lmedium under pressure is introduced with water under pressure by means of injectors 13.

'The continuously operating discharge system for the non-floating tailing product includes further cylindrical bottom section 22 connecting here with long vertical discharge pipe 23. The length of the pipe is adjusted to suit the sub-atmospheric pressure acting within the system. The lower end of pipe 23 is immersed into a pulp pool in open vessel 24 provided with overflow Weir 25. Pulp retained in vessel 24 and the pulp column in pipe 23 form a liquid seal for the system.

The top section of vessel 8 is further provided with cover 26 closing the vessel, froth collecting mean 27, open pressure equalizer pipe 28 and conduit 29 leading to cyclone 30. For continuous discharge of the concentrate pulp a parallel hydraulic system is provided including discharge pipe 31, vessel 32 and overflow weir 33. Conduit 34 connects cyclone 30 with any suitable source of vacuum (not shown).

Accessory apparatus not shown in FIGURE 1 may include c g. vacuum gages, pressure gages, vacuum and pressure equalizer vessels, instruments to measure and regulate flow rates of pulp, `water and air, pulp level indicators and means to regulate pulp levels, pumps, wash water sprays above the bubble column, means to add wash or dilution water, etc. Their use is obvious to a specialist in the art of flotation.

The unit apparatus shown in FIG. 2 differs from that already described in the following essential respects:

Vessel 8 is now provided with concentrate launder 35 placed on the outside of section 10. 4Launder 35 has a direct connection with discharge pipe 31. Conduit 29 originates from the top of cover 26.

With reference to FIG. 3, unit vessel 8 has no overflow means for the froth product. Instead, it is provided with conical top section 36 and substantially cylindrical bubble column section 37, which together with conduit 29 form a passage for the concentrate product to cyclone 30.

The apparatus shown in FIGURE l operates as follows:

Feed pulp pre-conditioned with reagents and preaerated under pressure in conditioner 1 ows via outlet 6 at a steady rate controlled l'by valve 7 into flotation chamber 8. Gas precipitation and nuclei formation on collector coated particles take place immediately. Aided by the upward flow of bubbles originating from gas introduced by injectors 13 into the lower part of pulp body in vessel 8, froth forms a bubble column in section 10. Within the said column, further rearrangement of particles takes place. Collector coated oatable particles proceed upward with the froth flow while particles of other minerals caught in the froth slide downward in the inter-bubble liquid layers. This downward movement can be, if desirable, aided by spraying wash solution onto the bubble column. The liquid -seeping downward in a substantially countercurrent fashion carries `away the unwanted particles. Concentrate product of extremely high quality results.

The concentrate product overflows into collecting means 27 and is drawn with carrier gas into cyclone 30, where solids and liquid are separated in the yform of pulp from gas. Concentrate pulp is discharged in a continuons stream via pipe 31 into vessel 32 and finally over Weir 33, while the gas fraction is drawn and discharged via the vacuum means out of the apparatus.

The tailing product is discharged via a parallel hydraulic system including pipe 23, vessel 24 and weir 25. Pulp level within flotation chamber r8 is automatically kept substantially constant by the simple overflow means shown in FIG. l. The coarse tailing fraction can be drawn olf via opening 20 controlled by adjustable plug 21.

Various other minor aspects regarding the apparatus and the operation are obvious to a specialist in the art of flotation.

Regarding operation of the unit apparatus shown in FIG. 2, it is seen that the concentrate product overowing the upper rim of section 10v is collected by launder 35 surrounding section 10, is transferred by gravity downward along the sloping bottom of launder 35, and is drawn olf directly into discharge pipe 31. Cyclone 30 prevents primarily the froth product from reaching the vacuum means in case of accidental overfrothing.

The operation of the unit apparatus shown in FIG. 3 deviates from those already described in that there is no froth overflow means to control the height of the froth layer within vessel 8. Rather, froth developed and particles caught in the froth are removed as shown with the flow into cyclone 30, where the concentrate pulp is separated from carrier gas as already explained.

In order to perform flotation operations under subatmospheric pressure at temperatures above the normal, conditioning and flotation units can be provided with heating elements of any suitable construction.

Any number of the unit otation processes described in the preceding can Ibe grouped within a variety of closed systems. In principle, such systems comprise flotation operations performed in such a way that the froth product from a given otation step is transferred to a successive step performed on a higher elevation and producing higher grade concentrate with the stream of evacuated Agas medium While the tailing product from the latter operation is returned by gravity to the prior operation lperformed on a lower elevation.

Referring now to FIGURE 4, corresponding multiple step closed circuit apparatus is shown to include five separate flotation chambers 38, 39, 40, 41, and 42 lall in the same closed system and under a common head of vacuum or partial vacuum. Chambers 38 and 39 are rougher flotation units, chamber 40 a cleaner flotation unit and chambers 41 and 42 scavenger flotation units.

For introduction of the original feed from conditioner 1, rougher units 38 and 39 are provided with feed inlet pipes 6 with rate control valves 7 substantially as has already been shown in FIG. 1.

In order to establish -a closed circuit system, the following additional conduit means are provided between the flotation chambers shown:

Conduits 43 and 44 for transfer of rougher flotation concentrate from units 38 and 39, resp., into cleaner flotation unit 40,

Conduits 45 and 46 for -discharge of cleaner flotation tailing into rougher flotation units 38 and 39, resp.,

Conduits 47 and 48 for discharge of rougher flotation tailings from units 38 and 39 into scavenger flotation units 41 and 42, resp., as feed material to the scavenger units, and

Conduits 49 and 50 for transfer of the scavenger concentrate from scavenger units 41 and 42 into rougher flotation units 38 and 39, resp.

It can be seen -from FIGURE 4 that the vacuum conduit means connecting -any two flotation chambers situated on different levels form also conduit means for the transfer of the froth product from a unit on a lower elevation to a unit on a higher elevation. For the gravitational return of the tailing product from a unit on a higher elevation to a unit on a lower elevation the flow arrangement is basically the same as shown in FIG. 1. The only essential difference is that discharge pipe 23 has now been replaced by substantially horizontal conduit means such as 45, 46, 47, and 48 connecting discharge sections 22 with corresponding feed section 9.

In other respects the multiple step closed circuit apparatus consists of means already described.

The multiple step closed circuit flotation system shown in FIGURE 4 operates as follows:

Pre-'conditioned and pre-aerated feed pulp is drawn at a desired pulp density and at a desired temperature by the existing pressure difference from one or more conditioner tanks 1 situated here on a lower level via Ifeed inlet pipes 6 at rates controlled by valves 7 into rougher flotation units 38 and 39 where separation into rougher concentrate and rougher tailing products takes place as Valready described. In the case shown, rougher concentrates drawn via conduits 43 and 44 are combined in cleaner flotation chamber 40. Cleaner flotation concentrate is drawn via conduit 29 into cyclone 30 where concentrate pulp is separated from the carrier gas as already explained. Cleaner tailing pulp flows by gravity from chamber 40 via conduits 45 and 46 into rougher flotation chambers 3'8 and 39, resp. The rougher tailings produced in units 38 and 39 flow by gravity via similar conduits 47 and 48 into scavenger flotation Iunits 41 and 42, resp. Scavenger concentrates are drawn to the corresponding rougher units situated on a higher elevation as shown. Scavenger tailing products are discharged via pipes 23.

Additional gas medium is introduced into the pulp pool of each flotation unit as already explained. l

It is obvious that many ways exist for grouping the apparatus operating under a common head of vacuum or partial vacuum. The basic ways include means to group flotation chambers:

In such a way that the vacuum conduit means leading to the rougher flotation chamber receiving the original feed forms also a conduit for transfer of the froth product from the said rougher flotation chamber to a cleaner flotation chamber situated on a higher elevation while the tailing withdrawal means attached to the bottom part of the cleaner flotation chamber forms a conduit for the cleaner tailing product back to the rougher flotation chamber;

In such a way that the tailing withdrawal means attached to the bottom part of the rougher floaton chamber receiving the original feed forms a conduit for transfer of the rougher tailing product to a scavenger flotation chamber situated on a lower elevation while the vacuum conduit means leading to the scavenging flotation chamber forms also a conduit for the froth product from the said scavenger flotation chamber to the said rougher flotation chamber;

In such a way that the vacuum conduit means leading to the rougher flotation chamber receiving the original feed forms also a conduit for transfer of the froth product from the said rougher flotation chamber -to a cleaner flotation chamber situated on a higher elevation while the tailing withdrawal means attached to the bottom part of the cleaner flotation chamber forms a conduit for the cleaner tailing product back to the rougher flotation chamber, the tailing withdrawal means attached to the bottom part of the rougher flotation chamber forming a conduit for the rougher tailing product to a scavenger flotation chamber situated on a lower elevation while the vacuum conduit means leading to the scavenger flotation chamber forms also a conduit for transfer of the froth product from Ithe said scavenger flotation chamber to the said rougher flotation chamber.

For reasons of expediency, vacuum conduit means other than those shown in FIGURE 4 may be added between units where needed. The conduits may naturally be provided with valves controlling the rates of flow to any desired extent.

As special examples it can be mentioned that for a low grade copper ore from which a small amount of concentrate only can be separated, one final cleaner unit may accept the concentrates from e.g. six similar rougher units situated around it on a lower level. For each rougher, one similar scavenger unit can be provided on a level below the roughers. On the other hand for a high grade iron ore from which a large percentage of concentrate is produced, a stepped combination of one cleaner, one rougher and one scavenger unit each of a similar size may form the basic group. Many other combinations are obvious to a specialist in the art of flotation.

The apparatus described in this specification is the only apparatus ever introduced allowing flotation in a great variety of combinations along the principles applied in many processes of chemical engineering. Some of the features new in the field of flotation include:

A flotation plant of an entirely new concept, yet of simple and sound construction,

All phases of operation can be controlled by instruments,

A flotation plant fully automated and run by computers can be foreseen,

Utmost cleanliness of operation,

Utmost simplicity of operation,

Minimum number of motor-run units (essentially conditioners and vacuum pumps only),

Minimum wear of the apparatus,

Minimum energy consumption,

Flotation at elevated temperature offers unexplored possibilities due to lowering of the temperature of the boiling point of water; at a pressure of mm. Hg, it is about 51 C., and

Flotation of products producing bad odors possible.

Finally it should be stated that the process and apparatus described in this specification are basically applicable to any separation by flotation that can be conducted by means of the conventional flotation process and in conventional open agitation-froth flotation units. In addition they can be used for flotation concentration of very finely divided particles where the conventional means are either poor or fail completely. It is clear that reprocessing of many of the flotation concentrates now produced in conventional flotation plants all over the world along the principles described in this specification will result, with or without further size reduction, in nal products of greatly improved quality.

What we claim is:

1. A 4froth flotation process comprising grouping a plurality of flotation cells in a closed circuit, subjecting said cells to a common sub-atmospheric pressure, and transferring the froth product produced in a given flotation cell with the gas medium evacuated therewith to a separate retreatment flotation cell performed on a higher elevation and producing a higher grade concentrate, and returning the tailing product produced in said latter retreatment cell by gravity to said given flotation cell performed on a lower elevation.

2. Apparatus for froth flotation, comprising a plurality of flotation unit chambers including a cleaner flotation chamber and rougher flotation chambers, means for introducing original feed into said rougher flotation chambers, said cleaner flotation chamber being positioned on a higher elevation than said rougher flotation chambers, said chambers being operatively grouped together under common sub-atmospheric pressure, first conduit means joining said cleaner flotation chamber with said rougher flotation chambers, said rst conduit means serving as vacuum conduits for imposing said sub-atmospheric pressure within said rougher flotation chambers and said first conduit means also serving as means for transferring the froth product from said rougher flotation chambers to said cleaner flotation chamber, second conduit means connecting the bottom of said cleaner flotation chamber with said rougher flotation chamber, said second conduit means serving to transport tailing product from said cleaner flotation chamber to said rougher flotation chamber.

3. Apparatus for froth flotation comprising a plurality of flotation unit chambers including rough flotation chambers and scavenger flotation chambers, said scavenger flotation chambers being positioned on a lower level than said rough flotation chambers, said chambers being operatively grouped together under common sub-atmospheric pressure, means to introduce original feed into said rough flotation chambers, first conduit means connecting the bottoms of said rough flotation chambers with said scavenger chambers, said first conduit means serving to transport tailing product from said rough flotation chambers to said scavenger chambers, and second conduit means connecting scavenger flotation chambers with said rough flotation chambers, said second conduit means serving as vacuum conduits for imposing sub-atmospheric pressure on said scavenger flotation chambers and also serving for transfer of the froth product from said scavenger flotation chambers to said rough flotation chambers.

4. Apparatus for froth flotation comprising a plurality of flotation unit chambers including, cleaner flotation chambers, rougher flotation chambers and scavenger flotation chambers, means for introducing original feed into said rougher flotation chambers, said cleaner flotation chamber `being positioned on a higher level than that of said rougher flotation chamber, and said scavenger flotation chamber -being positioned on a lower level than that of said rougher flotation chamber, said chambers being operatively grouped together under common subatmospheric pressure, first conduit means connecting the interior of said rougher flotation chambers with the interior of said cleaner flotation chamber, said first conduit means serving as vacuum conduits for imposing subatmospheric pressure on said rougher flotation chambers and also serving as means for transporting the froth product from said rougher flotation chambers to said cleaner flotation chamber, second conduit means connecting the bottom of the interior of said cleaner flotation chamber with the interior of said rougher flotation chambers for transporting the tailing product from said cleaner flotation chamber back to said rougher flotation chambers, third conduit means connecting the bottom of the interiors of said rougher flotation chambers with the interiors of said scavenger flotation chambers for transporting the tailing product from said rougher flotation chambers to said scavenger flotation chambers, and fourth conduit means connecting the interiors of said scavenger flotation chambers with the interiors of said rougher flotation chambers, said fourth conduit means serving as vacuum conduits for imposing sub-atmospheric pressure on said scavenger flotation chambers and also serving as means for transporting the froth product from said scavenger flotation chambers to said rougher flotation chambers.

References Cited UNITED STATES PATENTS 807,503 12/ 1905 Schwarz 209-166 1,022,085 4/ 1912 Hyde 209-166 1,176,428 3/ 1916 Callow 209-170 X 1,212,566 1/ 1917 Schiechel 209-166 1,221,990 4/1917 Holden 209-164 X 2,914,173 11/1959 Le Baron 209--166 2,984,348 5/ 1961 Adams 209-12 3,307,790 3/1967 Cohn 209-3 X FOREIGN PATENTS 505,688 5/ 1939 Great Britain.

621,414 2/ 1927 France.

692,499 8/ 1964 Canada.

703,922 France.

HARRY B. THORNTON, Primary Examiner.

ROBERT HALPER, Assistant Examiner.

U.S. Cl. X.R. 

